Search

Enteric septicemia of catfish (ESC), caused by the gram‐negative enteric bacteria Edwardsiella ictaluri, is a significant threat to catfish aquaculture in the southeastern United States. Antibiotic intervention can reduce mortality; however, antibiotic use results in an imbalance, or dysbiosis, of the gut microbiota, which may increase susceptibility of otherwise healthy fish to enteric infections. Herein, recovery of the intestinal microbiota and survivability of channel catfish in response to ESC challenge was evaluated following a 10‐day course of florfenicol and subsequent probiotic or prebiotic supplementation. Following completion of florfenicol therapy, fish were transitioned to a basal diet or diets supplemented with a probiotic or prebiotic for the remainder of the study. Digesta was collected on Days 0, 4, 8 and 12, beginning on the first day after cessation of antibiotic treatment, and gut microbiota was characterized by Illumina sequencing of the 16S rRNA gene (V4 region). Remaining fish were challenged with E. ictaluri and monitored for 32 days post‐challenge. Florfenicol administration resulted in dysbiosis characterized by inflated microbial diversity, which began to recover in terms of diversity and composition 4 days after cessation of florfenicol administration. Fish fed the probiotic diet had higher survival in response to ESC challenge than the prebiotic (p =.019) and negative control (p =.029) groups. [ABSTRACT FROM AUTHOR]

To prevent catfish idiopathic anaemia, diets fortified with iron have been adopted as a regular practice on commercial catfish farms to promote erythropoiesis. However, the effects of prolonged exposure of excess dietary iron on production performance and disease resistance for hybrid catfish (Ictalurus punctatus × I. furcatus) remains unknown. Four experimental diets were supplemented with ferrous monosulphate to provide 0, 500, 1000, and 1500 mg of iron per kg of diet. Groups of 16 hybrid catfish juveniles (~22.4 g) were stocked in each of 20, 110‐L aquaria (n = 5), and experimental diets were offered to the fish to apparent satiation for 12 weeks. At the end of the study, production performance, survival, condition indices, as well as protein and iron retention were unaffected by the dietary treatments. Blood haematocrit and the iron concentration in the whole‐body presented a linear increase with the increasing the dietary iron. The remaining fish from the feeding trial was challenged with Edwardsiella ictaluri. Mortality was mainly observed for the dietary groups treated with iron supplemented diets. The results for this study suggest that iron supplementation beyond the required levels does affect the blood production, and it may increase their susceptibility to E. ictaluri infection. [ABSTRACT FROM AUTHOR]

Objective: Proliferative gill disease (PGD) in Channel Catfish Ictalurus punctatus and hybrid catfish (Channel Catfish × Blue Catfish I. furcatus) is attributed to the myxozoan Henneguya ictaluri. Despite evidence of decreased H. ictaluri transmission and impaired parasite development in hybrid catfish, PGD still occurs in hybrid production systems. Previous metagenomic assessments of clinical PGD cases revealed numerous myxozoans within affected gill tissues in addition to H. ictaluri. The objective of this study was to investigate the development and pathologic contributions of H. ictaluri and other myxozoans in naturally and experimentally induced PGD. Methods: Henneguya species‐specific in situ hybridization (ISH) assays were developed using RNAscope technology. Natural infections were sourced from diagnostic case submissions in 2019. Experimental challenges involved Channel Catfish and hybrid catfish exposed to pond water from an active PGD outbreak, and the fish were sampled at 1, 7, 10, 12, 14, 16, 18, and 20 weeks postchallenge. Result: Nine unique ISH probes were designed, targeting a diagnostic variable region of the 18S ribosomal RNA gene of select myxozoan taxa identified in clinical PGD cases. Partial validation from pure H. ictaluri, H. adiposa, H. postexilis, and H. exilis infections illustrated species‐specific labeling and no cross‐reactivity between different myxozoan species or the catfish hosts. After experimental challenge, mature plasmodia of H. ictaluri and H. postexilis formed in Channel Catfish but were not observed in hybrids, suggesting impaired or delayed sporogenesis in the hybridized host. These investigations also confirmed the presence of mixed infections in clinical PGD cases. Conclusion: Although H. ictaluri appears to be the primary cause of PGD, presporogonic stages of other myxozoans were also present, which may contribute to disease pathology and exacerbate respiratory compromise by further altering normal gill morphology. This work provides molecular confirmation and more resolute developmental timelines of H. ictaluri and H. postexilis in Channel Catfish and supports previous research indicating impaired or precluded H. ictaluri sporogony in hybrid catfish. Impact statementThis work implicates Henneguya ictaluri as the primary cause of proliferative gill disease, a devastating parasitic disease of U.S. catfish aquaculture, but demonstrates other myxozoan parasites can contribute to disease severity. The study better defines the developmental timeline of H. ictaluri and H. postexilis in Channel Catfish and supports research indicating impaired maturation of H. ictaluri in hybrid catfish. [ABSTRACT FROM AUTHOR]

Bolbophorus damnificus is a digenetic trematode causing significant economic losses within the United States commercial catfish industry. The indirect life cycle is complex, requiring piscivorous birds, aquatic snails, and fish to complete. With federal protections on many piscivorous birds and no FDA‐approved therapeutic treatment for trematode infections in fish, management within the catfish industry is primarily limited to controlling the snail host. Planorbella trivolvis and Biomphalaria havanensis are snails commonly found in commercial catfish ponds and known to transmit B. damnificus. This study evaluated a low‐cost snail trap prototype for monitoring populations of these snails in efforts to better inform treatment regimes. Snail traps were deployed into ponds on a commercial catfish farm and checked weekly throughout the production season. All snails were identified and counted to evaluate trap efficacy. Traps captured significantly more snails in foodfish ponds than in fingerling ponds; however, this trend was not present in monthly box samples. B. havanensis was rarely collected and was only found consistently within one pond, while P. trivolvis was routinely collected from all ponds, although abundance varied widely among ponds. Snail traps could be a useful, low‐cost method to monitor snail populations within ponds and better inform control treatments. [ABSTRACT FROM AUTHOR]

The myxozoan Henneguya ictaluri is cited as the cause of proliferative gill disease (PGD) in Channel Catfish Ictalurus punctatus and Channel × Blue Catfish I. furcatus hybrids. Differences in host susceptibility result in decreased transmission rates, reduced sporogenesis, and lesser incidence of PGD in hybrid catfish. In experimental pond trials, continuous monoculture of hybrid catfish suppressed H. ictaluri abundance in pond systems compared to Channel Catfish monoculture. The present study examined differences in myxozoan community structure in catfish ponds stocked with Channel Catfish or hybrid catfish. Experimental ponds (0.4 ha) dedicated to Channel Catfish or hybrid catfish monoculture were maintained over three production cycles. Pond water collected during the spring of each year was subjected to metagenomic analysis by targeted amplicon sequencing of a diagnostic hypervariable region (DVR3) of the myxozoan 18S ribosomal RNA gene. Relative abundance of H. ictaluri was significantly greater in Channel Catfish ponds than in hybrid catfish ponds during years 2 and 3. In hybrid catfish ponds, H. ictaluri never exceeded 20% average relative abundance. Hybrid catfish ponds also revealed decreased myxozoan diversity and species evenness compared to Channel Catfish ponds, suggesting that myxozoan taxa associated with Channel Catfish may not be well adapted to the hybridized host. Results corroborate previous research indicating that hybrid catfish monoculture can suppress H. ictaluri compared to ponds that are devoted to Channel Catfish. These data imply that alternating catfish culture species in ponds (crop rotation) has the potential to mitigate PGD by precluding H. ictaluri from accumulating within ponds to levels associated with disease and catastrophic loss. Further, this work identified numerous previously unidentified taxa present within these systems that clustered phylogenetically with both catfish and noncatfish hosts. The impacts that these other myxozoans have on catfish health and production are unknown, but their presence indicates that myxozoan diversity within catfish aquaculture ponds has been greatly underestimated and is significantly influenced by stocking choice. [ABSTRACT FROM AUTHOR]

Avian piscivores cause direct economic losses to the aquaculture industry through predation, as well as indirect losses through transmission of digenetic trematodes. Bolbophorus damnificus is a trematode parasite associated with significant losses in catfish aquaculture. The complex life cycle involves the American white pelican Pelecanus erythrorhynchos, planorbid snails, and ictalurid catfish. With no approved therapeutics for B. damnificus in catfish Ictalurus spp. and federal protections on American white pelican, management is restricted to controlling snail hosts. Two snail species, marsh rams‐horn snail Planorbella trivolvis and ghost rams‐horn snail Biomphalaria havanensis, are common inhabitants of commercial catfish ponds and known to transmit B. damnificus. Previous work evaluated copper sulfate toxicity on marsh rams‐horn snails; however, data are lacking for ghost rams‐horn snails. Herein, laboratory‐reared adults of ghost rams‐horn snails and marsh rams‐horn snails were exposed to copper concentrations ranging from 0.16 to 3.38 mg/L Cu to evaluate 24‐, 48‐, and 72‐h acute toxicity. Additionally, sequential low‐dose treatments ranging from 0.1 to 0.8 mg/L Cu were evaluated on eggs, juveniles, and adults of ghost rams‐horn snails as a potentially safer treatment regime for ponds. Acute toxicity was similar between snail species for all exposure times. A 72‐h exposure produced an LC50 of 0.10 and 0.37 mg/L Cu for ghost rams‐horn snails and marsh rams‐horn snails, respectively. The LC50 values increased to 1.1 mg/L Cu for both species with 48‐h exposure. However, in the multiple low‐dose study, a single dose of 0.4 or 0.8 mg/L Cu was lethal to all adult snails after 1 week, as was 0.2 mg/L Cu after two doses. Four doses of 0.1 mg/L Cu or greater killed all ghost rams‐horn snail juveniles. Results indicate that marsh rams‐horn snails and ghost rams‐horn snails have similar sensitivity to copper, and multiple low‐dose treatments were effective against all life stages of ghost rams‐horn snails. These data indicate that copper can be an effective treatment for snail control in commercial catfish ponds. [ABSTRACT FROM AUTHOR]

Rotenone application has been reported to cause significant declines in zooplankton populations, with cladocerans and copepods being the most susceptible and possibly taking months to recover. Because copepods and cladocerans are preferred by fry of catfish Ictalurus spp., rotenone application could have significant effects on nursery pond production. Effects of rotenone on zooplankton and time required for recovery has not been studied in eutrophic aquaculture ponds typically drained and refilled yearly. We quantified rotenone application effects to either mostly drained ponds or full ponds (0.04 ha) in northwestern Mississippi on water quality, phytoplankton, zooplankton, and aquatic macroinvertebrates during May (23°C) and June (30°C) when most catfish fry ponds are stocked. For study 1, nine ponds were drained to about 15 cm of water. Six ponds were treated with 4 μL/L rotenone; three treated ponds were then treated with 4 mg/L potassium permanganate (KMnO4). The three additional ponds were drained but untreated. All ponds were then filled and fertilized with urea. In study 2, six full ponds were treated with 4 μL/L rotenone. Three of those ponds were then treated the next day with 4 mg/L KMnO4. An additional three ponds were left as untreated controls. Applying rotenone to the experimental ponds with 15 cm or less of water (study 1) had no effect on water quality, phytoplankton, or zooplankton. Neutralization with KMnO4 did not affect any measured variables. Desirable zooplankton numbers for catfish culture reached 100 organisms/L 11–14 d after treatment. In study 2, when a whole pond was treated with rotenone, desirable zooplankton numbers reached 100 organisms/L 7 d after treatment if neutralized with KMnO4 and about 11 d after treatment without neutralization. Rotenone treatment did not reduce predatory macroinvertebrate risk, and this should be addressed using additional management strategies. [ABSTRACT FROM AUTHOR]

In the mid‐2010s, Edwardsiella tarda was reaffiliated into three discrete taxa (E. anguillarum, E. piscicida, and E. tarda), obscuring previous descriptions of E. tarda‐induced pathology in fish. To clarify ambiguity regarding the pathology of E. tarda, E. piscicida, and E. anguillarum infections in US farm‐raised catfish, channel catfish (Ictalurus punctatus), blue catfish (I. furcatus), and channel × blue catfish hybrids were challenged with comparable doses of each bacterium. The most severe pathology and mortality occurred in fish challenged with E. piscicida, supporting previous reports of increased pathogenicity in commercially important ictalurids, while E. anguillarum and E. tarda warrant only minimal concern. Acute pathologic lesions among bacterial species were predominantly necrotizing and characteristic of gram‐negative sepsis but became progressively granulomatous over time. After 100 days, survivors were exposed to the approximate median lethal doses of E. piscicida and E. ictaluri, revealing some cross‐protective effects among E. piscicida, E. anguillarum, and E. ictaluri. In contrast, no fish that survived E. tarda challenge demonstrated any protection against E. piscicida or E. ictaluri. This work supports reports of increased susceptibility of channel, blue, and hybrid catfish to E. piscicida, while highlighting potential cross‐protective affects among fish associated Edwardsiella spp. [ABSTRACT FROM AUTHOR]

Edwardsiella piscicida is a growing problem for catfish aquaculture in the southeastern United States, particularly in channel (Ictalurus punctatus) x blue (I. furcatus) catfish hybrids. Research has shown E. piscicida isolates recovered from farmed catfish in Mississippi form at least five discrete phyletic groups, with no apparent differences in virulence in channel and hybrid catfish. Laboratory trials have shown a live‐attenuated E. ictaluri vaccine (340X2) cross‐protects against at least one E. piscicida isolate (S11–285) in channel and hybrid catfish, although it is unknown if this protection exists for other E. piscicida variants. To this end, channel and hybrid catfish were immunized by immersion with E. ictaluri 340X2. Thirty days later, fish were challenged by intracoelomic injection with representative E. piscicida variants from each phyletic group. Relative percent survival (RPS) for hybrids ranged from 54.7% to 77.8%, while RPS in channels ranged from 80.5% to 100%. A second study investigated whether channel and hybrid catfish exposed to heterologous E. piscicida isolates were similarly protected against wild‐type E. ictaluri. Fish were exposed by bath immersion to representative E. piscicida isolates from each phyletic group. Thirty days post‐immunization, fish were challenged by immersion with wild‐type E. ictaluri isolate S97–773. Regardless of variant, previous exposure to heterologous E. piscicida isolates significantly improved survival following E. ictaluri challenge. These findings suggest the presence of shared and conserved antigens among E. piscicida and E. ictaluri that could be exploited by application of polyvalent or cross‐protective vaccines. [ABSTRACT FROM AUTHOR]

Proliferative gill disease (PGD), caused by the myxozoan Henneguya ictaluri, is an important parasitic disease in U.S. catfish aquaculture. Continuous exposure of Channel Catfish Ictalurus punctatus to the actinospore stage of H. ictaluri results in a severe inflammatory response at the gills, leading to morbidity and death. Previous work indicates that the chemical cues in fish mucus that are recognized by myxozoan actinospores are not host specific. Building on these findings, the potential decoy effects of nonictalurid fish to actinospores of H. ictaluri were evaluated. Exposure of actinospores to gill mucus from multiple nonictalurid fishes resulted in actinospore activation for all fish species tested. Based on these findings, experimental transmission trials with potential interceptor fish were conducted. Individual Channel Catfish were co‐stocked with Western Mosquitofish Gambusia affinis at 0, 10, 25, or 50% of mean Channel Catfish biomass and exposed to 3,000 actinospores of H. ictaluri. Gill tissues were sampled at 24 h postchallenge, and parasite burden was estimated by H. ictaluri‐specific quantitative PCR. Results revealed that Western Mosquitofish stocked at 25% and 50% of catfish biomass reduced H. ictaluri DNA in Channel Catfish gills more than threefold. In a second study, catfish were exposed to pond water collected from an active PGD outbreak in the presence of Western Mosquitofish stocked at 25% of catfish biomass. Channel Catfish were sampled at 24 h and at 7 d after the last pond water exposure. At 24 h postexposure, catfish that were co‐stocked with Western Mosquitofish showed significantly lower H. ictaluri DNA than catfish stocked alone. This treatment effect was absent at 7 d postexposure, as parasite quantities within tissues had increased over 1,000×, with marked variability. Still, results indicate that the chemical cues that activate H. ictaluri actinospores are not specific to Channel Catfish. This work evinces a potential benefit of nonictalurid fish in combating H. ictaluri, suggesting that the presence of nonictalurid interceptor fish in catfish ponds may minimize PGD severity. [ABSTRACT FROM AUTHOR]

The US catfish industry has undergone significant technological advancements in an attempt to achieve cost efficiencies. This study monitored the progress of the adoption of alternative and complementary technologies in the US catfish industry. A 2019–2020 multi‐state in‐person survey in Alabama, Arkansas, and Mississippi (n = 68), revealed increased adoption of intensively aerated ponds (6,315 ha) and split ponds (1,176 ha). The adoption of alternative, more intensive, production practices has been accompanied by increased adoption of complementary technologies of fixed‐paddlewheel aeration, automated oxygen monitors, and hybrid catfish. As a result, the average aeration rate in the tristate region has increased to 7.8 kW/ha with 97% of catfish farms adopting automated oxygen monitors. About 53% of the water surface area in the tristate region was used for hybrid catfish production. Fingerling producers have also adopted a feed‐based, oral vaccine against Enteric Septicemia of Catfish, with 83% of the fingerling farms and 73% of the fingerling production area vaccinated against ESC in 2020. Increased adoption of productivity‐enhancing technologies in the US catfish industry explains the 59% increase in foodfish productivity from 2010 to 2019. Monitoring the progress of adoption of productivity‐enhancing technologies will guide researchers and Extension personnel involved in the refinement and dissemination of these technologies. [ABSTRACT FROM AUTHOR]

We compared the response to resource enhancement of a simple empirical model of intra‐guild predation (IGP) to the predictions of published, simple mathematical models of asymmetric IGP (a generalist IG Predator that feeds both on a specialist IG Prey and a Resource that it shares with the IG Prey). The empirical model was a food‐web module created by pooling species abundances across many families in a speciose community of soil micro‐arthropods into three categories: IG Predator (large predatory mites), IG Prey (small predatory mites), and a shared Resource (fungivorous mites and springtails). By pooling abundances of species belonging to broadly defined functional groups, we tested the hypothesis that IGP is a dominant organizing principle in this community. Simple mathematical models of asymmetric IGP predict that increased input of nutrients and energy to the shared Resource will increase the equilibrium density of Resource and IG Predator, but will decrease that of IG Prey. In a field experiment, we observed how the three categories of the empirical model responded to two rates of addition of artificial detritus, which enhanced the food of fungivores, the Resource of the IGP module. By the experiment's end, fungivore densities had increased ~1.5× (ratio of pooled fungivore densities in the higher‐input treatment to plots with no addition of detritus), and densities of IG Predators had increased ~4×. Contrary to the prediction of mathematical models, IG Prey had not decreased, but instead had increased ~1.5×. We discuss possible reasons for the failure of the empirical model to agree with IGP theory. We then explore analogies between the behavior of the empirical model and another mathematical model of trophic interactions as one way to gain insights into the trophic connections in this community. We also propose one way forward for reporting comparisons of simple empirical and mathematical models. [ABSTRACT FROM AUTHOR]

The bacterium Edwardsiella piscicida causes significant losses in global aquaculture, particularly channel (Ictalurus punctatus) × blue (I. furcatus) hybrid catfish cultured in the south‐eastern United States. Emergence of E. piscicida in hybrid catfish is worrisome given current industry trends towards increased hybrid production. The project objectives were to assess intraspecific genetic variability of E. piscicida isolates recovered from diseased channel and hybrid catfish in Mississippi; and determine virulence associations among genetic variants. Repetitive extragenic palindromic sequence‐based PCR (rep‐PCR) using ERIC I and II primers was used to screen 158 E. piscicida diagnostic case isolates. A subsample of 39 E. piscicida isolates, representing predominant rep‐PCR profiles, was further characterized using BOX and (GTG)5 rep‐PCR primers, virulence gene assessment and multilocus sequence analysis (MLSA) targeting housekeeping genes gyrb, pgi and phoU. The MLSA provided greater resolution than rep‐PCR, revealing 5 discrete phylogroups that correlated similarly with virulence gene profiles. Virulence assessments using E. piscicida representatives from each MLSA group resulted in 14‐day cumulative mortality ranging from 22% to 54% and 63 to 72% in channel and hybrid fingerlings, respectively. Across all phylogroups, mortality was higher in hybrid catfish (p <.05), supporting previous work indicating E. piscicida is an emerging threat to hybrid catfish aquaculture in the south‐eastern United States. [ABSTRACT FROM AUTHOR]

Bolbophorus damnificus has caused epizootics in catfish aquaculture since the mid‐1990s. To mitigate the losses that are associated with trematode infestations, research has focused on eradicating snails from ponds. Whole‐pond treatments with 0.64–1.27 mg/L Cu have been effective in killing snails; however, Cu can be toxic to fish and may result in oxygen depletions due to its algacidal properties. Given these constraints, the potential for repeated low doses of Cu as a safe, yet effective snail treatment was investigated. Adult marsh rams‐horn snails Planorbella trivolvis received four weekly doses of 0, 0.10, 0.19, 0.38, and 0.76 mg/L Cu. All of the snails died after the first treatment of 0.76 mg/L Cu. The lowest doses of 0.10 and 0.19 mg/L Cu resulted in 68% and 88% cumulative mortality, respectively. This experiment was repeated with laboratory‐reared adult marsh rams‐horn snails in two different laboratories, resulting in 100% mortality in the 0.38 mg/L Cu treatment. A second study evaluated the effects of repeated Cu doses on egg and juvenile snail survival. Two weekly doses of 0.19 mg/L Cu were enough to kill embryos, and all of the doses ≥0.05 mg/L Cu prevented the snails from hatching. In a pond trial, 0.51 mg/L Cu killed 100% of the adult snails after two doses. The lowest dose of 0.13 mg/L Cu killed 60% of the snails after three doses. Repeated weekly doses <0.38 mg/L Cu may reduce adult snail populations, prevent eggs from hatching, and be safer for fish than a single dose of 0.64–1.27 mg/L Cu. These data also suggest that weekly doses <0.05 mg/L Cu may suppress marsh rams‐horn snail populations by limiting hatching and impeding juvenile survival. [ABSTRACT FROM AUTHOR]

The trematode Bolbophorus damnificus (Digenea: Bolbophoridae) has caused significant economic losses since the late 1990s, with deleterious effects on production efficiency in farm‐raised catfish. Previous work has demonstrated that even mild outbreaks, which may go unnoticed by producers, can result in over 60% reduction in net economic returns. Although transmission rates in Channel Catfish Ictaluruspunctatus and hybrid catfish (Channel Catfish × Blue Catfish Ictalurus furcatus) are similar in controlled studies, anecdotal industry reports imply that the impacts of B. damnificus on hybrid catfish are less severe. In this study, mortality in juvenile Channel and hybrid catfish exposed to B. damnificus was evaluated in two discrete, replicated infectivity challenges. Mortality curves in Channel and hybrid catfish were consistent with trends previously established for B. damnificus in Channel Catfish, although in both challenges cumulative mortality was significantly lower in hybrids. All exposed fish presented clinical signs consistent with B. damnificus infection—namely lethargy, exophthalmia, distended abdomens, and metacercariae grossly visible below the skin. No mortality occurred and no parasites were observed in control fish. The biological and economic implications of these findings on catfish production are unknown but suggest that hybrid catfish are less susceptible to the deleterious effects and reduced productivity elicited by B. damnificus in Channel Catfish. [ABSTRACT FROM AUTHOR]

Blue catfish alloherpesvirus (BCAHV) is a novel virus isolated from the blue catfish (Ictalurus furcatus). To date, the ultrastructure, virulence and immunogenicity of BCAHV have not been reported. Given the importance of blue catfish in producing channel ♀ (I. punctatus) × ♂ blue (I. furcatus) catfish hybrids and the increasing demand for hybrid catfish in the US catfish industry, the susceptibility of blue, channel and hybrid catfish to BCAHV was assessed. Further, the cross‐protective potential of BCAHV against Ictalurid herpesvirus 1 (IcHV1) was investigated in channel and hybrid catfish that survive BCAHV exposure. Neutralization assays revealed BCAHV is refractive (neutralization index [NI] = 0) to anti‐IcHV1 monoclonal antibody Mab 95, compared to IcHV1 (NI = 1.8). Exposure of blue catfish fingerling to 1.3 × 105 TCID50/L BCAHV produced cumulative mortality of 51.67 ± 0.70% and pathologic changes similar to those of channel catfish virus disease. No mortality was observed in channel or hybrid catfish. Twenty‐eight days post‐challenge, surviving channel and hybrid catfish were exposed to 9.4 × 104 TCID50/L IcHV1 (LC50 dose), resulting in 100% relative per cent survival compared to naïve cohorts. These data provide baseline information for BCAHV and lay the groundwork for future studies. Data also identify BCAHV as a potential vaccine candidate against IcHV1. Based on host range and immunogenicity evaluations, in addition to genome sequence data from previous studies, BCAHV should be given consideration as a new species of Ictalurivirus. [ABSTRACT FROM AUTHOR]

Avian predation in catfish aquaculture has been a persistent issue throughout the history of the industry, and as production has expanded predation from piscivorous birds has intensified. Catfish ponds in the Mississippi River delta (in the Mississippi migratory flyway) provide a constant and readily accessible supply of forage for birds. Intensive foraging by fish‐eating birds has led to a specific regulatory policy and numerous on‐farm and regional management efforts. However, in 2016, legal challenges lead to recision of some federal policies and uncertainty as to allowable management, resulting in limitations on bird depredation. Estimating the extent of fish losses to avian predators is difficult, as loss estimates from farms are often confounded with disease‐ and management‐related mortalities. This study details the reported losses to birds that were observed in commercial‐scale catfish ponds at the Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi, during periods of limited bird management. The observed fish losses attributed to birds ranged from 33% to 95% loss in survival and potential yield losses of 4,396 to 8,889 lb/acre, increasing production costs and decreasing net returns. Net economic losses when accounting for negative net returns and lost profits ranged from US$3,518 to $4,060/acre. Losses of this magnitude on commercial fish farms are economically detrimental, especially because catfish farms lack the compensatory economic relief programs that are available in other agriculture sectors. Roost dispersal activities that are organized by federal agencies and avoiding delays in issuing bird depredation permits are vital for mitigating this persistent and growing regulatory problem in the U.S. catfish industry. [ABSTRACT FROM AUTHOR]

Bolbophorus damnificus (Digenea: Bolbophoridae) causes significant losses in US catfish aquaculture. Little is known regarding the prevalence of infected snail hosts during outbreaks. To assess prevalence of snails observed shedding Bolbophorus spp. cercariae, as well as snails that were infected but not observed shedding cercariae, Planorbella trivolvis (n = 8,159) were collected from 14 catfish production ponds with B. damnificus activity in Mississippi, USA. Individual snails were placed in 10 ml of filtered (20 μm) reservoir pond water and observed for 48 hr for cercariae release. Identification of B. damnificus or Bolbophorus sp. type II cercariae was confirmed by duplex PCR. Genomic DNA was isolated from ~100 non‐shedding snails from each pond and the PCR assay used to identify the presence of B. damnificus or Bolbophorus sp. type II infected snails. The prevalence of snails shedding B. damnificus ranged from 0.23 to 13.6%. Observation of cercariae shedding underestimated true B. damnificus and Bolbophorus sp. type II prevalence in 42.9 and 64.3% of sampled ponds, respectively. Prevalence of B. damnificus infected snails was typically <3%, indicating numbers of infected snails during outbreaks are low and mitigation efforts may be successful simply by reducing snail numbers and not require complete eradication. [ABSTRACT FROM AUTHOR]

Multiple‐batch production is the most widely practiced method of raising channel catfish. Producers are increasingly adopting intensified production practices in multiple‐batch systems by increasing stocking density and aeration rates as a means to improve cost efficiencies. Proven stocking recommendations are required for the efficient implementation of recent developments in multiple‐batch production. Twelve 0.4‐ha ponds were understocked with 17,484, 20,612, and 26,124 fingerlings/ha (mean weight = 40 g/fish) over equal weights of carryover fish (0.46 kg/fish @ 4,589 kg/ha). Fish were fed once daily to apparent satiation with a 28% protein floating feed and aerated with a single 7.4‐kW electric paddlewheel aerator. Density‐dependent significant differences were absent for gross, net, daily net yields, marketable yields (≥0.54 kg), growth (g/day), and survival. Sub‐marketable yield (<0.54 kg) and feeding rate increased significantly with increased understocking density. Economic analysis revealed increased breakeven prices and diminished net returns with increased stocking density when sub‐marketable fish were not considered as revenue. These differences in production costs and profits among the three treatments became minimal when sub‐marketable fish were included as revenue. All three density treatments attained positive annual net cash flows. This study validates channel catfish understocking densities of 17,000–26,000 fish/ha to improve cost efficiency in intensively aerated, multiple‐batch production systems. [ABSTRACT FROM AUTHOR]

The commercial channel catfish (Ictalurus punctatus) industry is adversely impacted by enteric septicemia of catfish (ESC), caused by the Gram‐negative enteric rod Edwardsiella ictaluri. In efforts to develop more effective management strategies, the use of a live‐attenuated E. ictaluri isolate as an oral vaccine was investigated. The utility and broad application of a vaccine is dependent on the protection offered against multiple field isolates. Immunization trials, followed by bacterial challenge with archived virulent E. ictaluri isolates from the catfish farming region of the southeastern United States, were conducted over a 3‐year period. These isolates were archived from 1993 to 2016 and included representatives from nonvaccinated and vaccinated populations of diseased channel catfish in Mississippi, an isolate from nonvaccinated hybrid catfish raised in Mississippi, and an isolate from nonvaccinated channel catfish from Alabama. Molecular characterization of the isolates revealed a high degree of genetic similarity evidenced by repetitive sequence‐mediated polymerase chain reaction (rep‐PCR) fingerprinting and virulence gene amplification, suggesting that the population of E. ictaluri within catfish aquaculture in Mississippi and Alabama has been genetically stable over time. Plasmid profiling revealed the existence of at least four distinct plasmids among field isolates. Nevertheless, the E. ictaluri vaccine protected fish against all isolates, irrespective of heterogeneous or homogeneous plasmid profiles. In addition, plasmid profiles were supported by antimicrobial sensitivity testing, indicating that the E. ictaluri vaccine strain does not carry natural or plasmid‐mediated multidrug resistance to the three antibiotics approved for use in U.S. food fish aquaculture. Challenge data from this study argue against the need for multivalent E. ictaluri vaccines to account for presumed antigenic or genetic variation among wild‐type E. ictaluri isolates as the vaccine was effective against all archived isolates. [ABSTRACT FROM AUTHOR]

Azomite is a hydrated sodium calcium alumina silicate that is mined from a volcanic deposit in Utah. The product contains many micronutrients that may be beneficial in preparing catfish nursery ponds for stocking. In northwest Mississippi, a 5‐week study was conducted to compare water quality, phytoplankton populations, and zooplankton populations in Channel Catfish Ictalurus punctatus nursery ponds treated with Azomite at 0, 50, or 100 kg/ha. The study was conducted in 0.04‐ha ponds during April, when fry ponds are prepared for stocking. Azomite application did not affect ammonia concentrations. Over time, nitrite concentrations increased more in control ponds compared to Azomite‐treated ponds; however, nitrite concentrations were low in all ponds. Chlorophyll‐a concentrations were also unaffected by Azomite application. The pH did significantly increase with increasing Azomite application rate. Azomite application had no effects on phytoplankton or zooplankton populations. Overall, there were no beneficial effects of adding Azomite to Channel Catfish nursery ponds in northwest Mississippi. [ABSTRACT FROM AUTHOR]

A pond study examined the effects of long‐term restricted feeding followed by full feeding on production and processing characteristics, fillet composition, and economics of market‐size hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. Market‐size fish averaging 674 g were stocked into 24 ponds (0.04 ha) at 17,300 fish/ha. Fish were either fed once or twice weekly for 4 months or once or twice weekly for 4 months followed by 15‐ or 30‐day daily full feeding. All fish were fed to apparent satiation on days fed. Fish fed once weekly for 4 months gained about 30% weight and those fed twice weekly gained 70% weight. Feeding once or twice weekly for 4 months followed by 15‐ or 30‐day full feeding did not significantly affect carcass yield compared with the initial sample (overwintered fish). At least 30 days of full feeding were needed to restore fillet yield to normal levels. Based on economic analysis and processing yield, it is suggested fish fed once weekly should be given full feed for 15 days or so to improve fillet yield before harvest. Fish fed twice weekly can be harvested with or without 15 days full feeding. [ABSTRACT FROM AUTHOR]

Proliferative gill disease (PGD) caused by the myxozoan Henneguya ictaluri is one of the most damaging diseases affecting U.S. catfish aquaculture. In channel and hybrid catfish, continuous exposure to the actinospore stage of the parasite elicits a destructive branchitis, impairing osmoregulatory and respiratory function. Mortality can reach 100% in severe outbreaks. Despite similarities during acute stages of infection, research indicates arrested development in hybrid catfish, evinced by reduced H. ictaluri sporogenesis and comparably less parasite DNA in hybrid tissues across the developmental timeline. To assess these findings at the pond level, 18, 0.4‐ha ponds were stocked (3,000 fish/pond) with channel (n = 9) or hybrid (n = 9) catfish fingerlings and maintained as monoculture systems for three production cycles, with clean harvests and restocking as warranted. Water was collected monthly for quantitative polymerase chain reaction (qPCR) estimations of H. ictaluri DNA, and sentinel fish were utilized to estimate PGD severity. By the second year, H. ictaluri DNA in hybrid systems was significantly reduced, and PGD lesions in sentinel fish were negligible. Assessment of parasite loads in fish harvested at the termination of the study revealed H. ictaluri DNA in channel catfish to be an order of magnitude higher than hybrid catfish. These results support previous work suggesting that the production of hybrid catfish may reduce PGD incidence in U.S. catfish aquaculture. [ABSTRACT FROM AUTHOR]

Edwardsiella piscicida has emerged as an important pathogen of channel × blue catfish hybrids cultured in the southeastern United States. With increasing popularity of hybrid catfish and growing concern over E. piscicida, the crossprotective potential of a live‐attenuated E.ictaluri vaccine was evaluated. An immunization bath of E. piscicida (3 × 107 CFU/ml) protected channel catfish against immersion challenge of wild‐type E. ictaluri (1 × 107 CFU/ml) across multiple temperatures and feeding regimens (relative percent survival [RPS]: 89–100%). Channel catfish immunized orally with a live‐attenuated E. ictaluri vaccine/feed admix (3 × 107 CFU/g of feed) were protected against intracoelomic injections of both high (HD) (7.4x105 CFU/fish; RPS = 85%) and low doses (LD) (1.5 × 105 CFU/fish; RPS = 88%) of E. piscicida. Because of limited feed consumption during vaccination, oral immunization of hybrids was followed by a 30‐min immersion bath with cultured vaccine (5 × 106 CFU/ml). Combinatory oral/bath vaccination was ineffective against HD E. piscicida but was protective against LD E. piscicida (48% RPS) and E. ictaluri (96% RPS). Finally, naïve catfish that survived LD E. piscicida injections were protected against E. ictaluri immersion challenge (2 × 107 CFU/ml; RPS: Hybrids 55%; Channels 75%). Results suggest a live‐attenuated E. ictaluri vaccine can also protect channel and hybrid catfish against E. piscicida. [ABSTRACT FROM AUTHOR]

Since its recognition in the early 1980s, enteric septicemia of catfish (ESC), caused by the gram‐negative enteric Edwardsiella ictaluri, is one of the most significant pathogens affecting catfish aquaculture. In efforts to improve disease management in U.S. catfish aquaculture, a live‐attenuated ESC vaccine and method of in‐pond oral vaccine delivery was developed. This work evaluated the efficacy of the oral delivery platform using a live‐attenuated E. ictaluri vaccine under simulated commercial conditions. Channel catfish fingerlings were orally vaccinated approximately 40–50 days poststocking by mixing the attenuated vaccine with feed using a patent‐pending mechanized delivery system. Across three discrete years under varying evaluation methods, vaccination resulted in significant improvements in survival, feed conversion ratio, feed fed, and total yield. An economic analysis of experimental data suggests a significant positive net economic benefit from vaccination. After accounting for a projected cost of vaccination, the realized improvements in survival and yield resulted in an estimated benefit exceeding $3,500/ha ($1,400/acre) on fingerling operations. These results suggest vaccinating channel catfish fingerlings against ESC is an effective strategy to mitigate ESC‐related losses and can significantly improve production efficiency and profitability on catfish operations. [ABSTRACT FROM AUTHOR]

This study evaluated dietary protein concentrations and replacing fish meal with porcine meat and bone meal (PMB) for pond‐raised fingerling channel catfish, Ictalurus punctatus. Three diets were formulated to have 28, 32, or 35% protein using soybean meal, cottonseed meal, and fish meal as the main protein sources, respectively. A fourth diet contained 32% protein with fish meal being replaced with PMB. Analyzed protein concentrations were 29.7, 31.9, 34.4, and 31.1% on 90% dry matter basis, respectively. Small fingerlings (average initial weight: 2.0 g/fish) were stocked in 20 earthen ponds (0.04 ha) at 172,970 fish/ha and were fed once daily to apparent satiation for 98 days. There were no significant differences in total diet fed, gross yield, final weight, feed conversion ratio, survival, or condition factor among diets. There were also no significant differences in ammonia‐N, nitrite‐N, chlorophyll a, or desirable zooplankton concentrations in pond water of fish receiving different diets. Results show that a diet containing about 30% protein can support optimum growth of pond‐raised channel catfish fingerlings of 2 g and larger in fertilized ponds fed once daily to apparent satiation. PMB can completely replace fish meal in a 32% protein diet. Economic analysis suggests considerable cost savings by replacing fish meal with PMB and reducing protein concentrations in channel catfish fingerling diets. [ABSTRACT FROM AUTHOR]

Shifts in densities of apex predators may indirectly affect fundamental ecosystem processes, such as decomposition, by altering patterns of cascading effects propagating through lower trophic levels. These top–down effects may interact with anthropogenic impacts, such as climate change, in largely unknown ways.We investigated how changes in densities of large predatory arthropods in forest leaf‐litter communities altered lower trophic levels and litter decomposition. We conducted our experiment in soil communities that had experienced different levels of long‐term average precipitation. We hypothesized that altering abundances of apex predators would have stronger effects on soil communities inhabiting dry forests, due to lower secondary productivity and greater resource overexploitation by lower trophic levels compared to wet forests.We experimentally manipulated abundances of the largest arthropod predators (apex predators) in field mesocosms replicated in the leaf‐litter community of Iberian beech forests that differed in long‐term mean annual precipitation by 25% (three dry forests with MAP < 1,250 mm and four wet forests with MAP > 1,400 mm). After one year, we assessed abundances of soil fauna in lower trophic levels and indirect impacts on leaf‐litter decomposition using litter of understorey hazel, Corylus avellana.Reducing densities of large predators had a consistently negative effect on final abundances of the different trophic groups and several taxa within each group. Moreover, large predatory arthropods strongly impacted litter decomposition, and their effect interacted with the long‐term annual rainfall experienced by the soil community. In the dry forests, a 50% reduction in the densities of apex predators was associated with a 50% reduction in decomposition. In wet forests, the same reduction in densities of apex soil predators did not alter the rate of litter decomposition.Our results suggest that predators may facilitate lower trophic levels by indirectly reducing competition and resource overexploitation, cascading effects that may be more pronounced in drier forests where conditions have selected for greater competitive ability and more rapid resource utilization. These findings thus provide insights into the functioning of soil invertebrate communities and their role in decomposition, as well as potential consequences of soil community responses to climate change. [ABSTRACT FROM AUTHOR]

Arthropods in the leaf litter layer of forest soils influence ecosystem processes such as decomposition. Climate‐change models predict both increases and decreases in average rainfall. Increased drought may have greater impacts on the litter arthropod community. In addition to affecting survival or behaviour of desiccation‐sensitive species, lower rainfall may indirectly lower abundances of consumers that graze drought‐stressed fungi, with repercussions for higher trophic levels.We tested the hypothesis that trophic structure will differ between the two rainfall scenarios. In particular, we hypothesized that densities of several broadly defined trophic groupings of arthropods would be lower under reduced rainfall.To test this hypothesis, we used sprinklers to impose two rainfall treatments during three growing seasons in roofed, fenced 14‐m2 plots and documented changes in abundance from initial, pre‐treatment densities of 39 arthropod taxa. Experimental plots were subjected to either LOW (fortnightly) or HIGH (weekly) average rainfall based upon climate models and the previous 100 years of regional weekly averages. Unroofed open plots, our reference treatment (REF), experienced higher than average rainfall during the experiment.The two rainfall extremes produced clear negative effects of lowered rainfall on major trophic groups. Broad categories of fungivores, detritivores and predators were more abundant in HIGH than LOW plots by the final year. Springtails (Collembola), which graze fungal hyphae, were 3× more abundant in the HIGH rainfall treatment. Taxa of larger‐bodied fungivores and detritivores, spiders (Araneae), and non‐spider predators were 2× more abundant under HIGH rainfall. Densities of mites (Acari), which include fungivores, detritivores and predators, were 1.5× greater in HIGH rainfall plots. Abundances and community structure of arthropods were similar in REF and experimental plots, showing that effects of rainfall uncovered in the experiment are applicable to nature.This pattern suggests that changes in rainfall will alter bottom‐up control processes in a critical detritus‐based food web of deciduous forests. Our results, in conjunction with other findings on the impact of desiccation on arthropods and fungal growth, suggest that drier conditions will depress densities of fungal consumers, causing declines in higher trophic levels, with possible impacts on soil processes and the larger forest food web. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the effects of dietary azomite (0.25% or 0.50%) or sea salt (0.5% or 1.0%) on the growth performance and disease resistance of Channel Catfish Ictalurus punctatus. Channel Catfish fingerlings were fed diets that were supplemented with graded levels of azomite or sea salt for 9 weeks in trial 1 and for 5 weeks in trial 2. The growth parameters (weight gain and feed conversion ratio) and survival rate were determined at the end of the feeding trials. The resistance of the fish against Edwardsiella ictaluri infection was also evaluated in those that were fed diets containing 0.5% azomite or 1.0% sea salt in trial 2. The results showed that there was no significant difference in the growth performance of the fish that were fed azomite‐ or sea salt‐supplemented diets compared with control animals (P > 0.05). The mortality rate of Channel Catfish 28 d after the E. ictaluri challenge did not differ significantly between groups receiving different dietary treatments. The results indicate that dietary supplementation with azomite or sea salt at the tested levels had no significant effect on either growth performance or disease resistance against E. ictaluri in Channel Catfish fingerlings. [ABSTRACT FROM AUTHOR]

A pond production trial was conducted to evaluate the economics of raising Channel Catfish Ictalurus punctatus in intensively aerated ponds operated under the single‐batch cropping system. Channel Catfish fingerlings averaging 0.09 lb were stocked at 6,000, 8,000, 10,000, and 12,000 fish/acre with six replicate ponds (1 acre) per treatment. A treatment of hybrid catfish (♀ Channel Catfish × ♂ Blue Catfish I. furcatus) fingerlings stocked into five replicate ponds at 12,000 fish/acre was concurrently evaluated to compare the economic performance of hybrids and that of Channel Catfish. All ponds were provided with a fixed‐paddlewheel aerator (10 hp/acre) and were fed once daily to apparent satiation for 206 d. For Channel Catfish, the gross yield ranged from 6,562 to 9,039 lb/acre, showing nominally linear trends of increasing yield with stocking density. However, the same trend was not seen in the relationship between costs and stocking density: the highest breakeven price (US$1.07/lb) was associated with the lowest density treatment (6,000 fish/acre), and the least cost ($0.96/lb) was associated with the intermediate density of 8,000 fish/acre. Average annual net cash flows from all Channel Catfish treatments were insufficient to make the investment in intensive aeration profitable in the long run (10 years). The hybrid catfish treatment (12,000 fish/acre) outperformed all Channel Catfish treatments in terms of yield (17,542 lb/acre), which offset some of the fixed costs associated with intensively aerated ponds and resulted in a lower cost of production ($0.85/lb) and better long‐term returns (17%). This study indicated that Channel Catfish do not perform well—either biologically or economically—at densities greater than 8,000 fish/acre in single‐batch, intensively aerated ponds. The study reflects current industry trends, where integrated farms (farms with their own processing plants) with yield‐maximizing business objectives prefer raising hybrid catfish in single‐batch systems, while nonintegrated farms prefer raising Channel Catfish in multiple‐batch systems. [ABSTRACT FROM AUTHOR]

Henneguya ictaluri is the etiologic agent of proliferative gill disease (PGD) in farm‐raised Channel Catfish Ictalurus punctatus and hybrid catfish in the southeastern United States, and significant annual losses are attributed to this disease. Research suggests that H. ictaluri infection dynamics in Blue Catfish I. furcatus and hybrid catfish (Channel Catfish × Blue Catfish) differ from those in Channel Catfish. Two separate infectivity trials were conducted to investigate H. ictaluri development in Channel Catfish, Blue Catfish, and their hybrids. On two separate occasions with two different year‐classes, fish were exposed to pond water containing H. ictaluri actinospores and sampled weekly for 12 weeks (trial 1) or 14 weeks (trial 2). In trial 1, the presence of H. ictaluri was evaluated histologically and by quantitative PCR of fish tissues, including gills, blood, anterior kidney, brain, heart, liver, posterior kidney, spleen, and stomach. Henneguya ictaluri DNA was detected in significantly higher concentrations throughout multiple organ systems in the Channel Catfish compared to the hybrid catfish and Blue Catfish, with the gills having higher quantities. Myxospores were observed in Channel Catfish gill tissue at 8 weeks postexposure. No myxospores were observed in Blue Catfish or hybrid catfish. The second trial focused on gills only and yielded similar results, with Channel Catfish having significantly greater H. ictaluri DNA quantities than hybrids or Blue Catfish across all time points. Myxospores were observed in Channel Catfish beginning at 6 weeks postexposure and were found in 36% (58/162) of Channel Catfish sampled for molecular and histological analysis during weeks 6–14. Myxospores in hybrid catfish were sparse, with single pseudocysts observed in two hybrid catfish (1.2%) at 14 weeks postexposure. These results imply arrested development of H. ictaluri in hybrid catfish. As such, culture of hybrid catfish may be an effective management strategy to minimize the burden of PGD. [ABSTRACT FROM AUTHOR]

There is a trend toward the increased incidence and prevalence of Edwardsiella piscicida septicemia in US catfish aquaculture, particularly in channel ♀, Ictalurus punctatus, × blue ♂, I. furcatus, hybrid catfish. From 2013 to 2017, a total of 3242 disease case submissions were made to the Aquatic Research and Diagnostic Laboratory (ARDL) at the Thad Cochran National Warmwater Aquaculture Center in Stoneville, MS. Of these, 1400 (43.2%) were hybrids. E. piscicida was suspected in 138 (4.3%) of cases, the majority of which (89.1%) were from hybrid catfish. A molecular survey of these isolates confirmed the majority (92.0%) to be E. piscicida. Furthermore, cases of E. piscicida from hybrids submitted to the ARDL and the Aquatic Diagnostic Laboratory of the Mississippi State University College of Veterinary Medicine in Starkville, MS, were documented for gross lesions and histological analysis. Grossly, E. piscicida presents with small dermal ulcerations, a raised fluid‐filled cranial midline lesion that is frequently ulcerated, hemorrhage in the gills, exophthalmia, and abdominal distension. Internally, lesions include splenomegaly, straw‐colored ascites, renomegaly, and occasionally hemorrhagic intestines. Histopathological examination is in agreement with gross observations, and infected fish repeatedly demonstrate a mononuclear meningoencephalitis, hemorrhagic branchitis, splenitis, ulcerative dermatitis, granulomatous interstitial nephritis, and hepatitis coupled with a hemorrhagic enteritis. [ABSTRACT FROM AUTHOR]

Channel Catfish Ictalurus punctatus fry farmers are interested in treating ponds to prevent trematode infections. Control strategies rely on chemical treatments to reduce snail populations and break the trematode life cycle. On a commercial catfish fingerling operation, we evaluated water quality, zooplankton, phytoplankton, and fish production in catfish nursery ponds treated with 1.02‐mg/L Cu 21 d before fry stocking. These variables were also evaluated in controlled experimental ponds treated with 1.27‐mg/L Cu 21, 14, 7, or 1 d before stocking. In the on‐farm trial, copper sulfate treatment initially reduced phytoplankton and zooplankton populations, but communities recovered to adequate numbers at stocking. However, fry survival and revenue from ponds treated with copper sulfate were reduced relative to those from untreated ponds (survival: 17.7% versus 63.0%; revenue: $10,250 versus $27,467 per hectare). In the experimental pond study, free copper concentrations at fry stocking were 0.52 mg/L for the 1‐d interval between treatment and stocking, 0.10 mg/L for the 7‐d interval, 0.04 mg/L for the 14‐d interval, and 0.02 mg/L for the 21‐d interval. Similar results were observed in the experimental study, with lower survival in all treatment groups compared to controls; the lowest survival was observed in fry stocked 1 d after copper sulfate treatment. The cause of lower survival in copper‐treated ponds is unclear. With the exception of ponds stocked 1 d after copper treatment, lower survival was likely related to effects on environmental quality rather than direct copper toxicity. Regardless of the cause, until further work evaluates copper's environmental effects, copper sulfate should not be used in Channel Catfish nursery ponds during early developmental fry stages. [ABSTRACT FROM AUTHOR]

Understanding the factors that determine invasion success for non‐native plants is crucial for maintaining global biodiversity and ecosystem functioning. One hypothesized mechanism by which many exotic plants can become invasive is through the disruption of key plant–mycorrhizal mutualisms, yet few studies have investigated how these disruptions can lead to invader success. We present an individual‐based model to examine how mutualism strengths between a native plant (Impatiens capensis) and mycorrhizal fungus can influence invasion success for a widespread plant invader, Alliaria petiolata (garlic mustard). Two questions were investigated as follows: (a) How does the strength of the mutualism between the native I. capensis and a mycorrhizal fungus affect resistance (i.e., native plant maintaining >60% of final equilibrium plant density) to garlic mustard invasion? (b) Is there a non‐linear relationship between initial garlic mustard density and invasiveness (i.e., garlic mustard representing >60% of final equilibrium plant density)? Our findings indicate that either low (i.e., facultative) or high (i.e., obligate) mutualism strengths between the native plant and mycorrhizal fungus were more likely to lead to garlic mustard invasiveness than intermediate levels, which resulted in higher resistance to garlic mustard invasion. Intermediate mutualism strengths allowed I. capensis to take advantage of increased fitness when the fungus was present but remained competitive enough to sustain high numbers without the fungus. Though strong mutualisms had the highest fitness without the invader, they proved most susceptible to invasion because the loss of the mycorrhizal fungus resulted in a reproductive output too low to compete with garlic mustard. Weak mutualisms were more competitive than strong mutualisms but still led to garlic mustard invasion. Furthermore, we found that under intermediate mutualism strengths, the initial density of garlic mustard (as a proxy for different levels of plant invasion) did not influence its invasion success, as high initial densities of garlic mustard did not lead to it becoming dominant. Our results indicate that plants that form weak or strong mutualisms with mycorrhizal fungi are most vulnerable to invasion, whereas intermediate mutualisms provide the highest resistance to an allelopathic invader. One hypothesized mechanism by which exotic plants can become invasive is through the disruption of key plant–mycorrhizal mutualisms, yet few studies have investigated how these disturbances can lead to invader success. We examined how the strength of the mutualism between a native plant and mycorrhizal fungus affects resistance to plant invasion. We show that the mutualisms of intermediate strengths are most resistant to plant invaders. [ABSTRACT FROM AUTHOR]

Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, to "superdosing" of 6‐phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4‐ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4‐ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond‐raised hybrid catfish and had no beneficial effects on water quality. [ABSTRACT FROM AUTHOR]

Abstract: This study examined four experimental diets with different protein concentrations and sources for pond‐raised fingerling hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus. A 35% protein diet with fishmeal was used as the control diet. Test diets were 32 and 28% all‐plant‐protein diets and a 28% protein diet with porcine meat, bone, and blood meal. Small fingerlings with a mean initial weight of 2.9 g/fish were stocked into 20 earthen ponds (0.04 ha) at a density of 172,970 fish/ha. They were fed once daily to apparent satiation for 107 d. No significant differences were observed for total diet fed, gross yield, final weight, survival, or condition factor among dietary treatments. However, fish fed the 28 and 32% all‐plant‐protein diets had a significantly higher feed conversion ratio than fish fed the 35% protein diet with fishmeal. There were no significant differences in chlorophyll a and nitrite concentrations in the pond water, but ponds receiving the 35% protein diet had significantly higher ammonia than those receiving 28% protein diets. Economic analysis suggested potential cost savings by using low‐protein and all‐plant‐protein diets for hybrid catfish fingerling production. [ABSTRACT FROM AUTHOR]

Abstract: This study evaluated the efficacy of an oral live‐attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish (ESC) in channel and hybrid catfish. The vaccine was delivered one time orally by feeding fish a diet coated with an attenuated E. ictaluri isolate at four doses to deliver between 4 × 106 to 3.2 × 107 viable vaccine cells/g wet feed. Thirty‐five days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 30 d postchallenge. Mortality of nonvaccinated hybrids (85%) and nonvaccinated channel catfish (73%) was similar but significantly greater than all groups of vaccinated fish. In channel catfish, a trend toward increasing mortality with decreasing dose was observed. Mortality of channel catfish vaccinated with the lowest dose (26.6%) was significantly higher than fish vaccinated with the highest dose (14.1%) but similar to fish vaccinated at the intermediate doses (17.5 and 19.4%). In contrast, mortality of four doses of vaccinated hybrid catfish was similar and ranged between 10.4 and 14.0%. The data demonstrate that the attenuated E. ictaluri vaccine at all four doses tested is effective at reducing ESC‐related mortalities in hybrid and channel catfish. [ABSTRACT FROM AUTHOR]

Abstract: Bolbophorus damnificus (Digenea: Bolbophoridae) causes significant economic losses in catfish aquaculture in the southeastern USA. To determine mortality trends associated with B. damnificus exposure, three separate disease challenges were conducted. The first challenge exposed channel catfish, Ictalurus punctatus, fingerlings (7–13 cm) to approximately 285 B. damnificus cercariae/L, while the second exposed fish to approximately 215 cercaria/L. Fish were monitored for morbidity and mortality for 28 d. In both studies, mortality first occurred 8 d postchallenge (PC) and peaked at 9 and 10 d PC, respectively. Mortality had subsided by 14 d PC, with only sporadic mortality occurring >15 d PC. Dead and moribund fish presented with lesions consistent with B. damnificus infection. A third challenge was performed to record histological changes associated with parasite development from initial exposure up to the cessation of mortality. Catfish (2–5 cm) were exposed as described above to a range covering 0, 35, 70, 100, 150, 175, and 215 cercariae/L. Each day, two fish were sampled from each treatment. Mortality trends were consistent with previous challenges. The mortality window coincided with parasite encapsulation, neovascularization, and development of the host‐derived cyst, suggesting that morbidity and mortality are linked to host pathophysiological changes in response to metacercariae encapsulation. [ABSTRACT FROM AUTHOR]

Abstract: Members of the genus Edwardsiella are important pathogens of cultured and wild fish globally. Recent investigations into the phenotypic and genotypic variation of Edwardsiella tarda have led to the segregation of E. tarda into three distinct taxa: E. tarda, Edwardsiella piscicida, and Edwardsiella anguillarum. In catfish aquaculture in the southeastern USA, E. piscicida has been more commonly associated with disease than E. tarda or E. anguillarum, and recent research has demonstrated E. piscicida to be more pathogenic in channel catfish than E. tarda or E. anguillarum. Anecdotal reports from industry suggest an increased prevalence of E. piscicida associated with the culture of channel (♀) × blue (♂) hybrid catfish. This work investigated the comparative susceptibility of channel catfish, blue catfish, and their hybrid cross to molecularly confirmed isolates of E. tarda, E. piscicida, and E. anguillarum. There was significantly higher mortality in hybrid catfish compared to channel catfish following intracoelomic injection of E. piscicida. To our knowledge, E. piscicida is the first bacterial pathogen to demonstrate increased pathogenicity in hybrid catfish compared to channel catfish. [ABSTRACT FROM AUTHOR]

Mortality associated with Edwardsiella ictaluri infection is a serious impediment to the commercial production of fingerling Channel Catfish Ictalurus punctatus. A patented, live, attenuated, orally delivered vaccine has been developed that offers exceptional protection against E. ictaluri infection in both laboratory and small‐scale pond trials. Further vaccine development is contingent on the successful completion of large‐scale field trials that accurately reflect industry conditions. This current work focuses on the validation of fermentation protocols and the optimization of downstream processing procedures to produce sufficient quantities of vaccine to conduct commercial‐scale field trials. Eight vaccine serials were produced from a master seed stock (S97‐773‐340X2) in a 50‐L floor model fermenter over two consecutive years. Following fermentation, cells were harvested, concentrated 10‐fold, and cryogenically stored (−74°C). To assess processing protocols and determine shelf life of cryogenically stored vaccine, serials were tested for cell viability and vaccine potency at various intervals over 24 months. There were no significant differences in cell viability between the fresh vaccine and the stored frozen product. All serials provided a high level of protection (77–100% relative percent survival) against E. ictaluri infection in juvenile Channel Catfish and exhibited excellent poststorage viability. This data demonstrates that the live, attenuated, orally delivered vaccine can be stored at −74°C for at least 2 years with no reduction in cell viability or vaccine potency. Received May 17, 2016; accepted January 19, 2017 Published online April 4, 2017 [ABSTRACT FROM AUTHOR]

Production variables of hybrid catfish (Channel CatfishIctalurus punctatus× Blue CatfishI. furcatus) reared in nursery ponds and then stocked were compared between fish fed immediately after stocking (standard industry practice) and fish for which feeding was postponed after stocking. Ponds (0.04 ha) were stocked with swim-up fry at 10,000 fish/pond (250,000 fish/ha). At 2 weeks poststocking, fish in the postponed feeding treatment were significantly smaller than fish in the standard feeding protocol. Therefore, all ponds began receiving commercial diets after 2 weeks. At 2 weeks poststocking and continuing through 5 weeks poststocking, the average individual fish length and weight was greater for the standard feeding protocol than for the postponed feeding protocol. At harvest, there were no differences in production variables between the two feeding protocols. Unlike a previous study with Channel Catfish fry, where feed was withheld for 6 weeks without compromising production, noticeable deficiencies in hybrid catfish fry growth were observed after only 2 weeks of feed restriction. However, compensatory growth was observed, and postponed feeding did not result in differences in production variables observed 6 weeks poststocking. At the feeding rate and feed prices during this study, we observed feed savings of only US$38.75/ha by postponing feeding for 2 weeks. Received July 27, 2016; accepted November 4, 2016 Published online February 13, 2017 [ABSTRACT FROM PUBLISHER]

A 2 × 2 factorial experiment was conducted to examine the growth performance of pond-raised hybrid catfish (female Channel CatfishIctalurus punctatus× male Blue CatfishI. furcatus) fingerlings fed diets containing two levels of protein (35% or 32%) with two animal protein sources (fish meal or porcine meat, bone, and blood meal [PMBB]). Small hybrid catfish fingerlings with a mean initial weight of 2.0 g/fish (SD = 0.6) were stocked into 20 earthen ponds (0.04 ha) at a density of approximately 172,970 fish/ha, based on a sample count of 1,000 fish. The fish were fed once daily to apparent satiation for 113 d. Total weight of feed fed, gross yield, feed conversion ratio (FCR), condition factor, and observed mortality were not significantly affected by either dietary protein concentration or animal protein source. Results demonstrate that dietary protein levels can be reduced from 35% to 32% without compromising fish growth and FCR for hybrid catfish fingerlings raised from 2 to 71 g in a growing season. Porcine meat, bone, and blood meal may completely replace fish meal in the diet. At current feed prices, a 32% protein diet with PMBB can provide considerable savings compared with the 35% protein diet with fish meal that is now used in commercial hybrid catfish fingerling production. Received January 21, 2016; accepted April 19, 2016 [ABSTRACT FROM PUBLISHER]

The digenetic trematodeBolbophorus damnificusis a significant hindrance to the production of farm-raised catfish in the southeastern USA. Severe infections withBolbophorus damnificuscan result in death, but the real damage lies in mild to moderate infections, which can go unnoticed by producers. Research has shown even mild infections can inhibit production to the point of operating at a net loss. The ramshorn snailPlanorbella trivolvisis the first intermediate host forBolbophorus damnificusand is prevalent in most commercial catfish ponds in the Southeast. Management practices aimed at controllingBolbophorus damnificusinfections primarily focus on reducing snail populations in ponds. Other aquatic snail species are also commonly associated with commercial catfish ponds, although little is known about their contributions to trematode infections in catfish. In the summer of 2014, 804 snailsBiomphalaria havanensis(synonym:Biomphalaria obstructa) were collected from a single commercial catfish pond and screened for trematode infections. Seven of these snails (0.81%) were actively releasing cercariae identified molecularly asBolbophorus damnificus. These cercariae were subsequently used in infectivity trials with Channel CatfishIctalurus punctatusfingerlings (5–8 cm). Seven days postchallenge, fish were examined histologically for the presence of metacercariae, which were present in 13 of 15 (86.67%) surviving fish. This is the first report of naturally occurring infections ofBolbophorus damnificusin another snail species. Received July 23, 2015; accepted January 30, 2016 Published online May 25, 2016 [ABSTRACT FROM PUBLISHER]

A pond study was initiated to evaluate effects of no feeding, maintenance feeding, and refeeding on production and processing characteristics of market-size hybrid catfish (female Channel CatfishIctalurus punctatus× male Blue CatfishI. furcatus). Fish with an average weight of 644 g were stocked into 20 earthen ponds (0.04 ha) at 14,826 fish/ha at the end of May. They were either not fed (N2), fed once weekly (W2) to satiation for 2 months to simulate a long-term harvest delay, or fed daily (D2) to satiation. After 2 months fish in half the ponds in each of the two feed-restricted treatments were harvested, and all fish in the remaining ponds were fed daily for an additional month. After 2 months N2fish experienced a 14.3% weight loss compared with a weight gain of 6.7% for FW2fish. After 2 months both N2and W2fish had reduced visceral fat and fillet yield compared with fish fed daily, but there were no significant differences in visceral fat percentage and fillet yield between N2and W2fish. At the end of 3 months, there were no significant differences in weight gain, net yield, fillet yield, or visceral fat whether fish were previously not fed or fed once weekly for the first 2 months, but fish fed daily throughout had significantly higher visceral fat and marginally higher fillet yield. Feeding once weekly for 2 months followed by 1-month full feeding resulted in significantly higher feed conversion ratio than fish fed daily for 3 months. Results demonstrate feeding once weekly can generally maintain body weight of hybrid catfish. No feeding or feeding once weekly for 2 months does not affect survival but significantly reduces fillet yield. One month of full feeding following no feeding or maintenance feeding improves fillet yield relative to values before refeeding. Received July 16, 2015; accepted January 21, 2016 Published online June 15, 2016 [ABSTRACT FROM PUBLISHER]

This study evaluated the efficacy of an oral live attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish in 20 full-sib fingerling channel catfish families. The vaccine was delivered orally by feeding fish a diet coated with an attenuated E. ictaluri isolate. Sixty-nine days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 21 d postchallenge. Vaccinated fish had significantly lower mortality than nonvaccinated fish following challenge ( P < 0.001). Mortality of vaccinated fish was 1.7 ± 1.4% as opposed to 47.8 ± 28.7% in nonvaccinated fish. Relative percent survival ranged from 87.7 to 100% with an average of 95.2 ± 4.0% (± SE) among the 20 families of fish. There were significant differences in mortality among families in nonvaccinated fish ( P < 0.01) while there were no differences among vaccinated families of fish. Results indicate that the live attenuated E. ictaluri vaccine is effective at reducing mortality in channel catfish exposed to virulent E. ictaluri. These data demonstrate that genetic differences among healthy families of channel catfish are not major considerations in developing an effective vaccination program utilizing the oral vaccination platform described in this study. [ABSTRACT FROM AUTHOR]

Proliferative gill disease ( PGD) in catfish is caused by the myxozoan Henneguya ictaluri. The complex life cycle requires Dero digitata as the oligochaete host. Efforts to control PGD by eradicating D. digitata have been unsuccessful. Smallmouth buffalo, Ictiobus bubalus, ( SMB) are opportunistic bottom feeders and a putative option for controlling D. digitata. In 2011, 15 ponds (0.4 ha) were stocked with 5000 channel catfish, Ictalurus punctatus; 7 of these 15 ponds were also stocked with 300 SMB fingerlings. There were no differences in benthic invertebrate numbers or water quality variables between ponds with or without SMB. At harvest, there were no differences in percent survival, total weight, or catfish feed conversion ratio. In the second year, 18 ponds (0.4 ha) were stocked with 6000 channel catfish. Half the ponds were also stocked with 300 SMB. Sentinel fish were used to estimate disease severity, and pond water was collected for molecular estimation of H. ictaluri actinospore concentrations. Similar to the first year, there were no differences between treatments in any variable tested, including PGD severity in sentinel fish and parasite concentrations in pond water. Under these study conditions, presence of SMB did not have a measureable effect on PGD incidence, parasite density, or overall catfish production. [ABSTRACT FROM AUTHOR]

Although invasive plants are a major source of terrestrial ecosystem degradation worldwide, it remains unclear which trophic levels above the base of the food web are most vulnerable to plant invasions. We performed a meta-analysis of 38 independent studies from 32 papers to examine how invasive plants alter major groupings of primary and secondary consumers in three globally distributed ecosystems: wetlands, woodlands and grasslands. Within each ecosystem we examined if green (grazing) food webs are more sensitive to plant invasions compared to brown (detrital) food webs. Invasive plants have strong negative effects on primary consumers (detritivores, bacterivores, fungivores, and/or herbivores) in woodlands and wetlands, which become less abundant in both green and brown food webs in woodlands and green webs in wetlands. Plant invasions increased abundances of secondary consumers (predators and/or parasitoids) only in woodland brown food webs and green webs in wetlands. Effects of invasive plants on grazing and detrital food webs clearly differed between ecosystems. Overall, invasive plants had the most pronounced effects on the trophic structure of wetlands and woodlands, but caused no detectable changes to grassland trophic structure. [ABSTRACT FROM AUTHOR]

The combination of open facilities, moisture, and warm weather during channel catfish, Ictalurus punctatus, spawning season causes mosquito-infestation problems. A common solution to mosquito problems in hatcheries is to use mosquito repellents applied to exposed skin and clothing. DEET ( N, N-diethyl- m-toluamide) is the active ingredient in most personal insect repellents. We determined the 24-h acute toxicity of DEET to channel catfish fry. The toxicity test consisted of 10 sac fry in three replications of six concentrations (range: 157-478 μL/L) and a control. In addition to toxicity testing, a trial was conducted to determine the amount of active ingredient dispensed from two different applicators: a pump sprayer and an aerosol can. The 24-h lethal concentration ( LC10) was 274 ppm, and the 24-h LC50 was 345 ppm. The concentration required to kill 50% of the organisms was above the 100 ppm threshold to be considered practically non-toxic. The pump sprayer (98.11% active ingredient) dispensed 113.3 ± 0.57 mg (mean ± SEM) active ingredient per pump. The aerosol can (30% active ingredient) dispensed 526.8 ± 6.71 mg (mean ± standard error mean [ SEM]) active ingredient per second. In hatcheries where air movement by fans is not sufficient to control mosquitoes, using insect repellent products containing DEET should be safe. [ABSTRACT FROM AUTHOR]

Confirming the impacts of invasive plants is essential for prioritizing management efforts, but is challenging, especially if impacts occur below-ground and over long periods as hypothesized for woodland shrub invasions., For this reason, we developed a novel 'paired-point' framework capable of detecting the below-ground impacts of slow-growing invasive plants from short-term data sets in an investigation into the below-ground consequences of European buckthorn Rhamnus cathartica L. (hereafter buckthorn) invasions into Chicago-area woodlands. We measured differences between the members of 97 pairs of buckthorn-invaded and buckthorn-free points in 10 below-ground response variables ( RVs) that buckthorn is hypothesized to alter (listed below). We then modelled these differences (Δ RVs) in response to the severity of the invasion found at each invaded point. A relationship (linear or nonlinear) between a Δ RV and severity, that is slope ≠ 0, suggests a buckthorn-induced change. An intercept (value of Δ RV where severity = 0) different from zero suggests a pre-existing difference., Relating differences to an invasion gradient rather than simply noting their presence provided evidence that the higher levels of moisture, pH, total C, total N [ABSTRACT FROM AUTHOR]